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  • 1
    ISSN: 1573-6849
    Keywords: human bivalent 15 ; meiosis ; sex vesicle
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Using fluorescent in-situ hybridization, we investigated the positioning of different human bivalents at the pachytene stage of normal male meiosis. We showed that, in about 35% of nuclei, the pericentromeric region of bivalent 15 is closely associated with the sex vesicle (SV). This behaviour may be linked to the presence of three domains in the pericentromeric region of chromosome 15: a large imprinted domain, a nucleolar organizing region (NOR), and a heterochromatic block. In order to define the domains of chromosome 15 involved in this association, we analysed the meiotic behaviour of other bivalents with similar domains: human bivalent 11 and mouse bivalent 7, bearing imprinted domains, other human acrocentric bivalents bearing a NOR, and the human bivalents 1, 9 and 16 containing a heterochromatic region. None of these bivalents were as frequently associated with the SV as the human bivalent 15. Nevertheless, we suggest that the bivalent 15 heterochromatin may be responsible for the association because of two properties: its telomeric location on chromosome 15 and its strong sequence homology with the Yq heterochromatin. This phenomenon could explain the high frequency of translocations between the chromosome 15 and the X or Y chromosomes.
    Type of Medium: Electronic Resource
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  • 2
    Publication Date: 2012-02-03
    Description: We report on a palaeomagnetic study of upper Miocene sediments from the Amantea basin, located on the Tyrrhenian coast of Calabria. The magnetic mineralogy is dominated by greigite and subordinate magnetite in the Tortonian-Messinian clays (ten sites), and by hemoilmenite and magnetite in the underlaying sands and volcanic ashes (three sites), which have not been dated. Data from the Tortonian, Messinian clays pass both a reversal and a fold test, and define a 19° ± 11° clockwise rotation (with respect to the geocentric axial dipole field direction) for the whole basin. The variable amounts of westward declinations observed in the underlaying sands and volcanic ashes can be due to (1) a large counterclockwise rotation episode occurring before the clockwise rotation, (2) the effects of a transitional geomagnetic field in these rapidly deposited sediments, or (3) the observed complex magnetic mineralogy. The new results, when compared with previous palaeomagnetic studies from other Calabrian basins, show that the Neogene drifting of the Calabro-Peloritan block from the eastern margin of Sardinia to the present-day position was accompained by a (probably Pleistocene) 15-20° rigid clockwise rotation recorded in both the Tyrrhenian and Ionian margins. This tectonic regime is shown to be very different from the one observed by previous studies in the northern Tyrrhenian domain, where large rotation associated with thrust sheet activity in the external Apennines were coeval with the onset of an irrotational extentional regime in the Tuscan and Latium Tyrrhenian margins. Palaeomagnetism thus confirms the significant geodynamical differences between the southern and northern Tyrrhenian Sea spreadings.
    Description: Published
    Description: 327-334
    Description: JCR Journal
    Description: reserved
    Keywords: Calabria ; Neogene ; palaeomagnetism ; tectonics ; 04. Solid Earth::04.05. Geomagnetism::04.05.06. Paleomagnetism ; 04. Solid Earth::04.07. Tectonophysics::04.07.07. Tectonics
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Type: article
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  • 3
    Publication Date: 2022-05-30
    Description: We report on new palaeomagnetic and magnetic fabric analyses of mainly Upper Miocene sedimentary sequences from the external central Apennine fold and thrust belt (Molise area), where the principal compressive structures are clearly non-coaxial. The sampling was carried out on the E–W-oriented Matese–Frosolone thrust sheet, that for its geographical position and structural setting (superposition of thrusting, strike-slip and extensional tectonics since Late Miocene to present-day) represents a key structure for the comprehension of the Neogene–Quaternary evolution of the entire Molise area. Palaeomagnetic results suggest that the Matese–Frosolone thrust sheet counterclockwise rotated at least 35° after Messinian times. These data confirm that the present-day trend variability observed in the main compressional structures in the Apennine chain can be related to rotations about vertical axes rather than to changes in the stress field orientation, at least since Late Miocene times. Magnetic fabric analyses indicate that the studied sediments were subjected to very mild deformation, suggesting that the surface emergence of the thrust front of the Matese–Frosolone unit is located farther north, far from the studied area. Well-defined magnetic lineations of tectonic origin were only observed in sites close to localised belts of strike-slip deformation.
    Description: Published
    Description: 143-157
    Description: JCR Journal
    Description: reserved
    Keywords: Apennines ; palaeomagnetism ; anisotropy of magnetic susceptibility ; structural geology ; Neogene ; 04. Solid Earth::04.05. Geomagnetism::04.05.06. Paleomagnetism ; 04. Solid Earth::04.07. Tectonophysics::04.07.07. Tectonics
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Type: article
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